Electrographic printing tube having filamentary conductive target



June 26, 1962 H. MOSS ELECTROGRAPHIC PRINTING TUBE HAVING FILAMENTARY CONDUCTIVE TARGET Filed May 1, 1957 Y DEFLECTION CIRCUIT IN VEN TOR.

HILARY MOSS AGENT United States Patent 3,041,611 ELECTROGRAPHIC PRINTING TUBE HAVING FILAMENTARY CONDUCTIVE TARGET Hilary Moss, Malvern, Pa., assignor to Burroughs Corporation, Detroit, Mich., a corporation of Michigan Filed May 1, 1957, Ser. No. 656,319 11 Claims. (Cl. 346-74) This invention relates to electrographic printing apparatus and it refers more particularly to the use in such apparatus of a two dimensional field of closely spaced pin-type printing electrodes, with means for moving an electron beam across the field to energize electrodes lying along a selected path.

The electrographic printing process has been described, as to the basic features thereof, in co-pending patent applications Serial No. 320,592, filed November 14, 1952,

and Serial No. 443,646, filed July 15, 1954, as well as in other patent applications assigned to the present assignee, and also in technical journals. Briefly, this process comprises the deposition or formation of electrostatic charges on a charge-retentive medium which collectively constitute a latent image of the printed material, and the subsequent rendering of this image visible by the application of finely powdered pigmented material (ink) to the medium. The powdered ink adheres to the medium over the charged areas by electrostatic attraction to form a visible image which can be fixed by heat treatment or in other manner described in the cited patent applications.

The present invention is concerned principally with that part of the apparatus which controls the printing of the latent electrostatic image. Printing occurs by the production of silent non-disruptive discharges between a printing electrode or electrodes and opposed base or anvil electrode means. The printing electrodes and the op posed anvil are spaced from one another to form a gap into which a printing medium in sheet form can be introduced to receive electrostatic charges as a result of interelectrode discharges. The printing electrodes may be small pins, for example, 0.003 inch in diameter. By the energization of selected ones of a group of these pins, patterns of dot-shaped electrostatic charges may be produced on the recording medium to form characters, graphs, etc.

According to the present invention a two dimensional field of closely spaced pin-type printing electrodes is provided in the face of a specially constructed cathode ray tube. Energization of these electrodes occurs by the impingement of the beam of the tube thereon. For printing purposes this beam can be deflected to impinge on electrodes positioned along any desired path by well known means such as are normally employed to produce luminous patterns on the face of the tube.

It is an object of the invention to provide improved electrographic printing apparatus wherein a two dimensional field of closely spaced pin electrodes is available for selective energization of the electrodes in accordance with an electrostatic charge pattern to be printed on a charge-retentive medium.

Another object is to provide in electrographic printing apparatus an improved construction and mounting for pin electrodes in a two dimensional field.

Another object is to provide means for selectively energizing electrodes of a two dimensional field of pin electrodes by means of the defiectable beam of a cathode ray tube.

Other objects and advantages of the invention will be apparent upon consideration of the following specification taken in connection with the accompanying drawings, in which:

3,041,611 Patented June 26, 1962 FIG. 1 is an elevational view of electrographic printing apparatus in accordance with the invention;

FIG. 2 is a front view of the face of the cathode ray tube shown in FIG. 1;

FIG. 3 is a section taken along the line 3-3 of FIG. 1, together with certain electrical circuit details;

FIG. 4 is a fractional enlarged sectional view of the face of the cathode ray tube as seen in FIG. 1.

FIG. 5 is a view similar to FIG. 4 showing a modified form of pin electrodes in the tube face, and;

FIG. 6 is a fractional view similar to FIG. 2 showing a portion of the printing electrode field and indicating certain electrodes energized to form a character.

Referring now to FIG. 1 there is shown a printing medium 11 in sheet form which may be transported, either continuously or intermittently between supply roll 13 and take-up roll 15 by means not shown. Anvil or base electrode 17 serves both as a guide for sheet 11 and as one of the electrodes between which printing discharges occur. While anvil 17 is illustrated as a single member it may alternatively take the form of a plurality of mutually insulated anvil means, each cooperative with and opposed to a selected printing electrode or group of printing electrodes. In such case the several anvil electrode means may be independently controllable as to the potential thereof. The surface of medium 11, facing away from electrode 17, is adapted to retain electrostatic charges and for this purpose may have a coating of a suitable dielectric material, such as polyethylene.

Cathode ray tube 21 may be of conventional design except as to the face 23 thereof, to -be described in detail later. In common with conventional tubes it includes an emissive cathode 25, accelerating electrodes 27 and two pairs of opposed electrostatic beam deflecting electrodes 29 and 31 respectively. An electron beam-forming potential is applied to cathode 25 from a high voltage source 33, and an accelerating potential may be applied to electrodes 27 by means not shown. Cathode heater means are omitted in the figure.

The end wall or face 23 of tube 21 is formed in a special manner of special glass and may be fabricated as a separate part, later welded to the body of the tube. A preferred type of glass for this purpose is a photo-sensitive glass manufactured by the Coming Glass Works, and sold under the trade name of Fotoform. This glass has the property of greatly increased solubility in certain solvents such as hydrofluoric acid solutions after exposure to light of certain wave lengths, followed by heat treatment. By an etching process chemical machining" of this glass is possible, including the drilling of fine holes therein. Hole drilling is done by exposing a thin sheet of the glass to ultraviolet light under a negative of the desired pattern of holes, followed by a prescribed heat treatment. The light-affected areas are then etched completely through the glass by immersion in a hydrofluoric acid solution. Details of the process have been published in Industrial and Engineering Chemistry, January 1953, p. 115, and in sales bulletins of the Corning Glass Works.

Two types of holes can be formed in the sheet according to the manner of applying the etching agent. If =ap plied to one face, only, a somewhat conical hole is etched in which the side may form an angle with the axis of the hole of from about 5 to 30, determined by control of the etching process. This is illustrated by the shape of the holes and electrodes therein in FIG. 4. If etched part way from each surface of the sheet, substantially cylindrical holes can be produced as illustrated in FIG. 5.

In the case of face 23 of tube 21 a two-dimensional field of holes is produced, as seen in FIG. 2, in which the individual holes may have a diameter of the order of 0.001 inch to 0.005 inch, and in which the hole spacing may be of the order of 0.003 inch to 0.010 inch, by way of example, only. To form the pin electrodes, after etching, these holes may be filled with a hardening metallic paste, such as an amalgam, which adheres to the boundaries of the holes and upon hardening forms a minute pin-type electrodes in each hole. The application of the paste may be under considerable pressure, it necessary, and the filaments of paste need not extend completely through the tube face, it being necessary only that the electrodes produced thereby are so formed that they can be energized, interiorly of the tube, by the electron beam. In addition to amalgams, a further example of conducting material for filling the holes in the face of tube 21 is a paste comprising an epoxy resin monomer which has had mixed therewith a high proportion, say at least 50 percent, of powdered metallic material. Such resinous material usually is cured at an elevated temperature. The tube face, with formed electrodes, is gas tight. Other methods of forming or inserting electrodes in the tube face may be employed.

For some applications conical electrodes, as electrodes 41 of FIG. 4, are preferred with the smaller of the two end surfaces used as the discharge surface. In other cases the cylindrical form of electrodes 43 of FIG. may be preferable. A number of such electrodes, energized to form the letter T, are designated by reference numeral 43E in FIG. 6. While in this figure the trace of the electron beam, as represented by the designated energized electrodes, is illustrated as being of the width of only one such printing electrode, in many instances the sectional area of the beam relative to that of an electrode and the electrode spacing will be such that the beam normally will energize a plurality of adjacent electrodes at a given instant, with the result that what appears to the eye as a single dot when the latent electrostatic image is developed, actually is a group of smaller elemental dots each due to printing discharge from a single printing electrode.

In FIG. 3 XVaxis deflection means 45 may be of conventional type for applying deflection potentials to electrodes 29, with similar Y axis deflection means 47 for applying potential to electrodes '31. Through the joint operation of means 45 and '47 the electron beam of tube 21 may be caused to trace any path long the face '23 of the tube and thereby to energize electrodes 43 positioned along such path.

In addition to the deflection of an electron beam of constant intensity and of sufiicient amplitude to produce a printing discharge between an electrode in the face of tube 21 and anvil means 17, a modulation means 49 may be employed for controlling the intensity of the beam and thereby controlling the charge density of the electrostatic dot images formed on medium 11. This may also serve to blank out the beam over appropriate intervals. Variation of the intensity of the electron beam of a cathode ray tube is sometimes known as Z axis modulation. By such ch-argeregulating means the amount of inking powder adhering to the electrostatic dot images may be varied so that gradations in tone may be produced as well as black and white effects in the finished record. This latter technique in addition to the dotshaped character of the elemental images, which need not be circular in form, furnishes a means for reproducing variabletone images such as half-tone pictures, as well as black and white representations of characters, graph-s, etc.

The above description of the apparatus of the invention is to be considered as illustrative, only, of one form which the invention may take. The scope of the invention is more fully defined in the appended claims.

What is claimed is:

1. In apparatus for electrostatic printing, base electrode means, means for feeding an electric-charge retentive medium across said base electrode means, a cathode ray tube having an evacuated interior and having an end wall upon which its electron beam impinges strong enough to bear external application of normal atmospheric pressure, said tube being mounted with respect to the base electrode means so that its end wall is positioned adjacent to but on the side of the medium opposite to the base electrode means, said tube further having means for projecting and controlling the sweep of an electron beam upon the inner face of its end wall, said end wall of the tube being formed of glass and being provided therethrough from the innner face to the outer face thereof with a multiplicity of minute apertures substantially uniformly distributed over a relatively wide area of the screen, said apertures each having a diameter in the order of .001 to .005 inch and being spaced apart from one another in the order of .003 to .010 inch, and an insert of hardened paste material in each of the apertures and forming a gas-tight closure therefor, the material constituting said inserts having an electrically conductive ingredient therein rendering the inserts electrically conductive and such that when the electron beam of the tube impinges on the inner ends of the inserts the outer ends thereof cooperate with the base electrode means to form discrete electric fields passing through the recording medium and electrically charging the same in accordance with the positions of the beam impinged inserts in the end wall of the tube.

2. In apparatus for electrostatic printing, base electrode means, means for feeding an electric-charge retentive medium across said base electrode means, a cathode ray tube being permanently intern-ally evacuated and having an end wall upon which its electron beam is directed for impingement sufficiently strong to bear external application of normal atmospheric pressure despite such internal evacuation, said tube being mounted with respect to. the base electrode means so that its end wall is positioned adjacent to but on the side of the medium opposite to the base electrode means, said tube having means for projecting and controlling the sweep of an electron beam upon the inner face of its end wall, said end wall being formed of glass and being provided therethrough from the inner face to the outer face thereof with at least one row of closely spaced apart minute apertures each having a diameter in the order of .001 to .005 inch and being spaced apart from one another in the order of .003 to .010 inch, and an insert of hardened paste material embedded in each of the apertures and forming a gas-tight closure therefor, the material of which said inserts are formed having an electrically conductive ingredient therein rendering the same electrically conductive and such that when the electron beam of the tube impinges on the inner ends of the inserts the outer ends thereof cooperate with the base electrode means to form discrete electric fields passing through the recording medium and electrically charging the same in accordance with the posititlrars of the beam impinged inserts in the end wall of the tu 3. In apparatus for electrostatic printing, base electrode means, means for feeding an electric-charge retentive medium across said base electrode means, a cathode ray tube having an end wall upon which its electron beam impinges and mounted with respect to the base electrode means so that its end wall is positioned adjacent to but on the side of the medium opposite to the base electrode means, said tube having means for projecting and controlling the sweep of an electron beam upon the inner face of its end wall, said end wall being formed of glass and being provided therethrough from the inner face to the outer face thereof with a multiplicity of extremely minute apertures closely and substantially uniformly dispersed over a relatively wide area of the end Wall, and an insert of hardened paste material embedded in each of the apertures and forming a gas-tight closure therefor, said hardened paste material having a metallic ingredient rendering the same electrically conductive'and such that when the electron beam of the tube impinges on the inner ends of the inserts thereof the outer ends thereof cooperate with the base electrode means to form discrete electric fields passing through the recording medium and electrically charging the same in accordance with the positions of the beam impinged inscrts in the end wall of the tube, said end wall being impervious to the gases of the atmosphere and suificiently strong to withstand rupture when one side thereof is subjected to ordinary atmospheric pressure and the other side thereof is exposed to a vacuum.

4. In apparatus for electrostatic printing, base electrode means, means for feeding an electric-charge retentive recording medium across said base electrode means, a cathode ray tube internally permanently evacuated and having an end wall strong enough to bear external atmospheric pressure and further having means for projecting and controlling the sweep of an electron beam upon the inner face of the end wall, said tube being mounted with respect to the base electrode means so that its end wall is positioned adjacent but on the side opposite to the medium from the base electrode, said end wall being formed of photosensitive glass and perforated by chemical ctching to provide at least one row of extremely minute apertures, electrically conductive material comprising a hardened plastic and an electrically conductive ingredient filling each aperture of the end wall and forming a gastight insert therefor, said filled apertures each having a diameter in the order of .001 to .005 inch and being spaced from one another in the order of approximately .003 to .010 inch, the electrically conductive inserts in said apertures forming extremely fine electrodes on the outer face of the end Wall, each of which when energized by the impingement of the electron beam thereon cooperates With the base electrode means to create an electric field passing through the recording member and electrically charging the same in accordance with the position of the energized insert on the end wall of the tube.

5. In apparatus for electrostatic printing, base electrode means, means for feeding an electric-charge retentive recording medium across said base electrode means, a cathode ray tube internally permanently evacuated and having an end wall strong enough to bear external atmospheric pressure and further having means for projecting and controlling the sweep of an electron beam upon the inner face of the end wall, said tube being mounted with respect to the base electrode means so that its end wall is positioned adjacent but on the side opposite to the medium from the base electrode, said end wall being formed of photosensitive glass and perforated by chemical etching to provide therethrough from the inner face to the outer face thereof at least one row of extremely minute apertures, a hardened paste including a metallic ingredient filling each aperture of the end wall and forming a gas-tight electrically conductive insert therefor, said filled apertures each having a diameter in the order of .001 to .005 inch and being spaced from one another in the order of approximately .003 to .010 inch, the electrically conductive inserts in said apertures forming extremely fine electrodes on the outer face of the end wall, each of which when energized by the impingement of the electron beam thereon cooperates with the base electrode means to create an electric field passing through the recording member and electrically charging the same in accordance with the position of the energized insert on the end wall of the tube, and means for modulating the electron beam of the cathode ray tube for varying the intensity of the electric fields created in the recording member and thus the intensity of the electrical charged areas thereof.

6. A cathode-ray tube face plate strong enough to bear the application of atmospheric pressure to one side thereof while the other side thereof is exposed to vacuum, comprising an impervious inorganic insulating layer pierced by a multiplicity of holes, a filling for the said holes comprising an organic plastic mixed with an inorganic electrically conductive filler, the said filling being hardened in place and hermetically sealed in said holes, the said face plate being adapted to be hermetically sealed to an evacuable envelope.

7. A cathode-ray tube having an electron beam impinging portion of its envelope strong enough to bear external atmospheric pressure while the interior thereof is evacuated and pierced with a multiplicity of holes each sealed hermetically with a filling comprising a hardened plastic and an electrically conductive filler.

8. A cathode-ray tube having an electron beam impinging portion of its envelope strong enough to bear external atmospheric pressure while the interior thereof is evacuated and pierced with a multiplicity of holes each sealed hermetically with a filling comprising an electrically conductive mixture of electrically non-conducting sealing material with electrically conductive material.

9. A cathode ray tube face plate strong enough to bear the application of atmospheric pressure to one side thereof while the other side thereof is exposed to vacuum, comprising: an impervious insulating layer pierced by a multiplicity of holes, each of said holes hermetically sealed with a filling comprising a hardened plastic and an electrically conductive filler, the said face plate being adapted to be hermetically sealed to an evacuable envelope.

10. A cathode ray tube face plate strong enough to bear the application of atmospheric pressure to one side thereof while the other side thereof is exposed to vacuum comprising: an impervious insulating layer pierced by a multiplicity of holes; each of said holes being sealed hermetically with a filling comprising an electrically conductive mixture of electrically non-conducting sealing material with electrically conductive material.

11. An apparatus for electrostatic printing comprising: a cathode ray tube having an end wall portion with inner and outer faces, said tube having means for projecting and controlling the sweep of an electron beam upon the inner face of said end wall portion; said end wall portion being formed of glass-like material and being provided therethrough, from said inner face to said outer face thereof, with a multiplicity of extremely minute apertures closely and substantially uniformly dispersed over a relatively wide area of the end wall portion, said end wall portion being impervious to the gases of the atmosphere and sufficiently strong to withstand rupture when one side thereof is subject to atmospheric pressure and the other side thereof is exposed to a vacuum; a plurality of inserts of hardened paste material with one each embedded in a different one of said apertures thereby forming a gas-tight closure therefor; said hardened paste material having a metallic ingredient rendering the same electrically conductive thereby adapting said end wall portion such that when the electron beam of the tube impinges upon the inner face ends of said inserts the outer face ends thereof are cooperable with an electric-charge retentive recording medium brought up adjacent to the outer face of the end wall portion to form discrete electrically charged areas thereon in accordance with the positions of the beam impinged inserts in the end wall portion of the tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,015,570 Sabbah et al. Sept. 24, 1935 2,091,152 Malpica Aug. 24, 1937 2,189,340 Donal Feb. 6, 1940 2,217,334 Diggory et a1. Oct. 8, 1940 2,262,123 Sukumlyn Nov. 11, 1941 2,273,793 Ekstrand Feb. 17, 1942 2,283,148 Bruce May 12, 1942 2,777,040 Kazan Jan. 8, 1957 2,777,745 McNaney Jan. 15, 1957 2,793,178 Morris May 21, 1957 FOREIGN PATENTS 1,077,037 France Nov. 3, 1954 

